Electric welding in car

Pretty much disconnect batteries.

when Awill4x4 off here has done work on mine hes always insisted on that.

I think you also need to place the Earth lead from the welder as close to the aria that is to be welded as possible.

Hi Chris,
As you mentioned disconect the batteries,do not hook up the earth to the exhaust as you could pit your big ends bearings if your unlucky,be carefull of combustables..fuel tank..lines.. batt..anything that might lite up and burn...pays to be a little over cautious if there's such a thing..if your doing overheads and your got a full lenght beard protect it...ive burnt chunks out of two of mine over the years.
Hope this helps.
JD

The main problem is the earth return to the welder. The current will always take the path of least resistance so if it has a choice of either going through a rusty / painted / poorly riveted or welded panle and some of your vehicle wireing then it will choose the wires every time. A lot of current traveling through small wires or even jumping across incredible small distances within some electronic components means trouble either now or in the future. Be aware that even if the current does not actually break over inside some electronic components it can (and does) 'stress' the small devices leading to a shortened service life. As has already been mentioned above, get a good clean earth as close to your work as possible and disconect the battery. The only 100% sure method of damageing electronics is to unplug them and remove them from the vehicle. That's almost impossible and most people do not have any problems if they carry out the above suggestions.

The issue is with voltage spikes frying the computer. Most places that regularly do welding on cars, ie exhaust shops, these days hook a diode pack across the battery to suppress spikes without disconnecting the battery. If you don't have a suitable suppressor then disconnect the battery. Shops don't disconnect as it means they then have to reprogram things like stereos etc. Also some vehicles lose their computer memory and have to be "retrained" (sounds like some co-workers i know;-) before the car will run again.

The computer plug should be disconnected as well as both battery terminals and yes get the earth as close as possible to the area being welded